Electrocatalytic investigation on the water oxidation ability of a hangman complex based on the [Ru(tpy)(bpy)(OH2)]2+ motif

Abstract

Many known single-site ruthenium complexes used in the catalytic water oxidation reaction react according to the WNA mechanism (WNA=water nucleophilic attack). During catalysis, a nucleophilic attack of a water molecule on a high-valent metal oxo species occurs and the efficiency is positively influenced by beneficial hydrogen-bonding interactions utilizing an external acid or base. Thus, installing a proton‐donor/acceptor functionality in proximity to the catalytic site should have a dramatic influence on the catalytic activity. We recently prepared a “hangman” version of the known [Ru(tpy)(bpy)(OH2)]2+ complex (bpy=2,2′-bipyridine, tpy=2,2′;6′,2″-terpyridine) in which a carboxylic functional group is placed close to the ruthenium center. This catalyst was initially investigated in homogeneous catalysis using cerium (IV) ammonium nitrate as sacrificial electron acceptor. Unfortunately, due to the acidic conditions used, the positive effect on the catalytic performance according to the base-assisted WNA mechanism was in fact hampered. Further investigations on heterogenized systems are presented herein and reveal a clear dependence of the catalytic activity on the solution pH.